The invention relates to biological activating water cleaning with fluid filtration with automatic return of activated sludge from the fluid filter back into the activation process and to arrangements for execution of said method.
Fluid filtration has become more and more the main intensification factor in the technology of biological water cleaning. A larger application of this progressive technique has, however, up to now been prevented by some operational difficulties; particularly, at small and very small arrangements and also the somewhat reduced efficiency of separation in the case of cleaning waste water containing nitrogenous compounds and requiring nitrification and denitrification. In addition, more and more expressively, a further intensification of the cleaning process of actual arrangements utilizing fluid filtration is of importance.
Operation difficulties are, for instance, experienced at reactors utilizing fluid filtration with closed cylindrical vessels. Said types of reactors are suitable for cleaning of local sources of sewage waters. Specific requirements for a solution to the problems associated with such arrangements follows both from a need for an automated operation and a need for high reliability. Moreover, there is also high requirements for incorporation of cleaning stations into an ecologically exposed environment, for instance, in a recreation center.
Other specific requirements follow from attempts to achieve comparable costs of water cleaning with costs of operation of large cleaning stations. Up to now, all known reactors with fluid filtration, offer certain drawbacks. Present solutions involving hydraulics of fluid filtration do not prevent clogging of the inlet slot which opens into the space for fluid filtration of small stations; that is, into the space for separation, with a following obstruction. This tendency for clogging of the separation space is common among methods of fluid filtration and among corresponding types of arrangements and is highly problematic especially when smaller capacities are concerned. In utilization of arrangements with fluid filtration where the separation space is accessible, removal of such a functional failure is easy and quick even without interruption of operation. In the case of a closed cylindrical reactor, it is, however, more difficult and requires putting the station out of operation.
With some types of cylindrical reactors, having a separation space dividing the space of the vessel into two activating spaces, another difficulty is experienced; in that "dead" zones are created in the lower part of the activating space below the level of the separating space; that is, those places having a tendency for sedimentation of the activated sludge. This sedimentation takes place particularly when the operation is interrupted, whereby the settled sludge cannot--due to the following aeration--be again taken along into the ascending stream by a stream of the activating mixture. This settled sludge starts at anaerobic conditions to decay and causes operational difficulties and a reduced efficiency of cleaning. In order to secure a corresponding flow at these "dead" zones, a rather demanding system of rectifying walls and an increased amount of power are required for a perfect suspension of the activated sludge. All that of course requires increased investment and operation costs.
Another drawback of actually known embodiments presented in the prior art, particularly those involving cylindrical reactors for biological water cleaning, is their limited capacity. An improvement requires either large vessel dimensions or restriction of their application for the smallest of cleaning stations.
In addition to said specific drawback of cylindrical reactors, all small cleaning stations have a common drawback, namely relatively higher specific costs for cleaning of waste water surpassing even multifold costs of larger and large cleaning stations both regarding the range of specific investment costs and also of operational costs.
The deciding share of costs for wages and attendance and maintenance is, for small cleaning stations, unproportionally high. Thus a rather important factor for said small stations is a complete automation and simultaneous reliability of operation, both of which have been, up to now, impossible to fully secure with prior art types of cylindrical cleaning stations with fluid filtration.
Another cause of a certain limitation in utilization of fluid filtration, is the reduced capacity of separation at a higher value of the sludge index; that is, in the situation involving the creation of a light activated sludge. A tendency to create an activated sludge of this kind requires many kinds of waste waters and operations of cleaning stations with introduced denitrification. As the reduction of the capacity of separation has an exponential character in dependence on the sludge index, a small increase of the value of the sludge index results in a substantial reduction of the capacity of said arrangement.
An increase of the capacity of separation thus represents a possibility of a substantial intensification of operation of cleaning stations, which in the case of known cleaning stations with fluid filtration, has not been fully utilized.
A substantial problem of cleaning stations with fluid filtration is frequently the so-called post-denitrification in the layer of the fluid filter caused by lack of oxygen in this layer. In an anoxidal medium of a fluid filter a post-denitrification takes place, whereby part of remnant nitrates are reduced by denitrification processes to gaseous nitrogen, which causes the flotation of sludge, the removal of which is complicated and frequently leads even to a reduction of quality of the cleaned water.